feat: implement dedicated package shop page with legal confirmation

This commit:
- Creates MobilePackageShopPage.tsx for listing packages and handling checkout.
- Implements a confirmation screen with mandatory AGB and Withdrawal checkboxes.
- Registers the new route /mobile/billing/shop.
- Updates EventAnalyticsPage to link to the new shop page.
- Reverts previous inline upgrade logic in BillingPage.tsx.

resources/js/admin/router.tsx

@@ -37,6 +37,7 @@ const MobileEventAnalyticsPage = React.lazy(() => import('./mobile/EventAnalytic
 const MobileNotificationsPage = React.lazy(() => import('./mobile/NotificationsPage'));
 const MobileProfilePage = React.lazy(() => import('./mobile/ProfilePage'));
 const MobileBillingPage = React.lazy(() => import('./mobile/BillingPage'));
+const MobilePackageShopPage = React.lazy(() => import('./mobile/PackageShopPage'));
 const MobileSettingsPage = React.lazy(() => import('./mobile/SettingsPage'));
 const MobileDataExportsPage = React.lazy(() => import('./mobile/DataExportsPage'));
 const MobileLoginPage = React.lazy(() => import('./mobile/LoginPage'));
@@ -213,6 +214,7 @@ export const router = createBrowserRouter([
           { path: 'mobile/notifications/:notificationId', element: <MobileNotificationsPage /> },
           { path: 'mobile/profile', element: <RequireAdminAccess><MobileProfilePage /></RequireAdminAccess> },
           { path: 'mobile/billing', element: <RequireAdminAccess><MobileBillingPage /></RequireAdminAccess> },
+          { path: 'mobile/billing/shop', element: <RequireAdminAccess><MobilePackageShopPage /></RequireAdminAccess> },
           { path: 'mobile/settings', element: <RequireAdminAccess><MobileSettingsPage /></RequireAdminAccess> },
           { path: 'mobile/exports', element: <RequireAdminAccess><MobileDataExportsPage /></RequireAdminAccess> },
           { path: 'mobile/dashboard', element: <MobileDashboardPage /> },